diff --git a/repos/libports/lib/mk/zlib.mk b/repos/libports/lib/mk/zlib.mk
index 7451c39ff3..a73b9bf962 100644
--- a/repos/libports/lib/mk/zlib.mk
+++ b/repos/libports/lib/mk/zlib.mk
@@ -5,6 +5,7 @@ SRC_C    = adler32.c compress.c crc32.c deflate.c gzclose.c \
            gzlib.c gzread.c gzwrite.c infback.c inffast.c inflate.c \
            inftrees.c trees.c uncompr.c zutil.c
 CC_WARN  =
+CC_OPT  += -DZ_HAVE_UNISTD_H
 
 vpath %.c $(ZLIB_DIR)